Method of making modified activated carbon

ABSTRACT

An activated carbon substrate which is pre-treated to make an exposed surface of the activated carbon substrate substantially hydrophilic, coated with a carbon precursor to form a coated activated carbon, and then the coated activated carbon substrate is heated to carbonize the carbon precursor to from the modified activated carbon. The modified activated carbon comprises a uniform porous carbon membrane formed on an exposed surface of the activated carbon substrate. The carbon membrane can mediate the absorption and/or adsorption kinetics of the activated carbon substrate. The modified activated carbon, which can be incorporated into one or more components of a cigarette, can selectively remove gaseous constituents from mainstream smoke during smoking.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Divisional patent application of U.S. patentapplication Ser. No. 11/727,712, filed Mar. 28, 2007 and claims priorityunder 35 U.S.C. §119(e) to U.S. provisional Application No. 60/787,498,filed on Mar. 31, 2006, the entire content of which are incorporatedherein by their references.

BACKGROUND

Conventional cigarettes have filter elements that may incorporatematerials such as carbon. Certain commercially available filtercigarettes have particles or granules of carbon (e.g., an activatedcarbon material or an activated charcoal material) incorporated with thecellulose acetate tow or in cavities between cellulose acetate material.However many materials, including activated carbon, that mechanically,chemically and/or physically remove constituents from mainstreamcigarette smoke are typically non-selective. These materials can removeconstituents that contribute flavor to mainstream smoke and, as aresult, can impart poor taste and/or off-taste during the smoking of acigarette. Accordingly, it would be desirable to provide a cigarettefilter element that is capable of removing certain gas phaseconstituents of mainstream cigarette smoke while not adversely affectingthe flavor of the mainstream smoke.

SUMMARY

According to one embodiment, a process for making modified activatedcarbon comprises an activated carbon substrate and a uniform, porouscarbon membrane formed on an exposed surface of the activated carbonsubstrate, the process comprising: (i) providing an activated carbonsubstrate; (ii) pre-treating the activated carbon substrate to make anexposed surface of the activated carbon substrate substantiallyhydrophilic; (iii) coating the activated carbon substrate with a carbonprecursor to form a coated activated carbon substrate; and (iv) heatingthe coated activated carbon substrate at a temperature sufficient tocarbonize the carbon precursor to form the uniform, porous carbonmembrane.

The modified activated carbon made according to the process comprisesthe activated carbon substrate and a uniform, porous carbon membraneformed on an exposed surface of the activated carbon substrate. Theactivated carbon substrate can be in the form of beads, granules, orfibers. Multiple coatings of carbon precursor can be applied andcarbonized to control the thickness and/or surface porosity of thecarbon membrane.

The activated carbon substrate can comprise particles of activatedcarbon, which can have an average particle size of from about 100microns to 5 mm or from about 200 microns to 2 mm. Preferably, theactivated carbon substrate has an average pore size of less than about500 Angstroms, or a pore size distribution comprising greater than about20% micropores (and fewer than about 80% mesopores), more preferablygreater than about 80% micropores. The surface area of the activatedcarbon substrate can be greater than 50 m²/g (e.g., greater than 200,500 or 1000 m²/g).

The pre-treating preferably comprises spraying the activated carbonsubstrate with and/or immersing the activated carbon substrate in anaqueous solution comprising a surfactant. A preferred surfactant iscetyltrimethylammonium chloride and a preferred pre-treatment solutioncomprises from about 1 to 99 wt. % surfactant, more preferably fromabout 1 to 25 wt. % surfactant.

After incorporating the surfactant in and/or on the activated carbonsubstrate, the activated carbon substrate can be dried preferably at atemperature of less than about 120° C. prior to coating with a carbonprecursor.

The coating preferably comprises spraying the pre-treated activatedcarbon substrate with and/or immersing the pre-treated activated carbonsubstrate in a solution comprising the carbon precursor. The coating canbe done at room temperature. Suitable carbon precursors includesaccharides, disaccharides, polysaccharides, fructose and ethylcellulose, and a preferred carbon precursor solution comprises fromabout 1 to 99 wt. %, more preferably between about 20 and 60 wt. %carbon precursor. A preferred carbon precursor is sucrose.

The carbon precursor can be incorporated in an amount to give from about1 to 150% by weight, preferably from about 20 to 80% by weight, of thecarbon precursor in and/or on the pre-treated activated carbonsubstrate.

After coating the activated carbon substrate, the coated substrate canbe dried at a temperature of less than about 120° C. and then heated,preferably at a temperature of from about 150° C. to 400° C. to form thecarbon membrane. The coated substrate is preferably heated in anoxidizing atmosphere (e.g., in air). After converting the carbonprecursor to the carbon membrane, the carbon membrane can comprise fromabout 1 to 150% by weight of the activated carbon substrate. The averagepore size at the surface of the modified activated carbon (i.e., thepore size of the carbon membrane) can be different than the average poresize at the surface of the activated carbon substrate. Preferably, themodified activated carbon has an average surface pore size that is atleast 25% less than the average surface pore size of the activatedcarbon substrate.

The carbon membrane forms a uniform porous coating on the activatedcarbon substrate and preferably covers at least 80% of the exposedsurface of the activated carbon substrate and/or the carbon membrane hasan average thickness having a standard deviation that is less than about25% of the average thickness. Preferably, the carbon membrane has anaverage thickness of from about 1 micron to 0.1 mm. By providing auniform porous carbon coating on the activated carbon substrate, thefiltration characteristics and/or mechanical integrity of the modifiedactivated carbon can be improved with respect to the activated carbonsubstrate. For example, the modified activated carbon may selectivelyremove targeted gas phase constituents from mainstream cigarette smokewhile advantageously producing less dust than the activated carbon.

According to another embodiment, a cigarette comprises modifiedactivated carbon particles. The modified activated carbon particles arepreferably incorporated in the filter element of the cigarette. However,the modified activated carbon particles can be located in othercomponents of the cigarette, such as in the tobacco cut filler.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a batch type fluidizing bed apparatus, which canbe used to treat activated carbon particles with a carbon precursor.

FIG. 2 is a diagram of a continuous type fluidizing bed apparatus, whichcan be used to treat activated carbon particles with a carbon precursor.

FIGS. 3A and 3B show SEM micrographs of as-received activated carbonparticles.

FIGS. 4A and 4B show SEM micrographs of modified activated carbonparticles.

FIG. 5 is a graph of percent delivery (relative to a control) of selectgas phase constituents as a function of sucrose content for modifiedactivated carbon.

FIG. 6 is a partially exploded perspective view of a cigarette whereinfolded paper containing the modified activated carbon is inserted into ahollow portion of a tubular filter element of the cigarette.

FIG. 7 is a partially exploded perspective view of a cigarette whereinthe modified activated carbon is incorporated in a plug-space-plugfilter element.

FIG. 8 is a partially exploded perspective view of a filter elementhaving modified activated carbon incorporated therein, which may be usedto form a cigarette that can be smoked in an electrically-heatedcigarette smoking system.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one embodiment, a process is provided for making modified activatedcarbon. The modified activated carbon comprises a uniform porous carbonmembrane on an activated carbon substrate. The process comprises (i)providing an activated carbon substrate; (ii) pre-treating the activatedcarbon substrate to make an exposed surface of the activated carbonsubstrate substantially hydrophilic; (iii) coating the activated carbonsubstrate with a carbon precursor to form a coated activated carbonsubstrate; and (iv) heating the coated activated carbon substrate at atemperature sufficient to carbonize the carbon precursor to form theuniform porous carbon membrane. The steps of coating the activatedcarbon substrate with a carbon precursor and heating the coatedactivated carbon substrate to form the carbon membrane can be repeatedto form a carbon membrane having the desired thickness, surface coverageand/or surface porosity.

Solutions comprising a compound used for the pre-treatment and/orsolutions comprising the carbon precursor can be applied to theactivated carbon substrate (e.g., particles of activated carbon) byspraying the carbon with a solution or by immersing the carbon in asolution. The pre-treatment compound and/or the carbon precursor can beincorporated in and/or on the activated carbon substrate via absorptionand/or adsorption.

According to a preferred method, an activated carbon substrate in theform of beads, granules or fibers can be introduced into a vessel,fluidized by introducing a fluidizing gas into the vessel, and thepre-treating or the coating can be carried out by introducing a solutionof at least one pre-treatment compound or at least one carbon precursorinto the vessel while the activated carbon substrate is in a fluidizedstate. Solutions of the pre-treatment compound and/or carbon precursorcan also be incorporated in and/or on the activated carbon substrateusing the incipient wetness technique wherein the activated carbonsubstrate is immersed in the solution for a specified period of time andthen dried.

The steps of pre-treating, coating and heating produce an activatedcarbon that is coated with a uniform layer of porous carbon (i.e.,modified activated carbon). The absorptive characteristics, adsorptivecharacteristics and/or mechanical properties of the modified activatedcarbon can be controlled by controlling the formation of the carboncoating. For example, the porosity of the carbon coating can control thekinetics of absorption/adsorption by the activated carbon substrate. Thecarbon membrane can reduce the amount of dust formed from the activatedcarbon substrate during processing (e.g., during incorporation of themodified activated carbon into one or more components of a cigarette),during cigarette storage and/or during smoking. Also provided arecigarette filters and cigarettes having the modified activated carbonincorporated therein.

By “activated carbon” is meant any porous, high surface area form ofcarbon. Activated carbon can be derived via thermal treatment of anysuitable carbon source. The activation treatment typically increases theporosity and activated carbon can be provided with a wide range of poresizes or the pore sizes can be controlled to provide a desired pore sizedistribution.

In a preferred embodiment, the activated carbon comprises granulatedcarbon particles ranging in size from about 100 microns to 5 mm. Forexample, the carbon particles can be carbon pellets having sizes ofabout 0.2 to 2 mm (e.g., about 200, 500, 1000 or 2000 microns).

The activated carbon substrate can have any desired pore sizedistribution that comprises pores such as micropores, mesopores andmacropores. The term “microporous” generally refers to such materialshaving pore sizes of about 20 Angstroms or less while the term“mesoporous” generally refers to such materials with pore sizes of about20-500 Angstroms. A preferred activated carbon substrate comprises 20%or more micropores (i.e., 80% or less mesopores). A more preferredactivated carbon substrate comprises at least 80% micropores. Bydepositing a carbon precursor and forming a carbon membrane on anexposed (e.g., external) surface of the activated carbon, the relativeratio of micropores, mesopores and macropores can be controlled in orderto control the absorptive and/or adsorptive selectivity of the modifiedactivated carbon with respect to selected gaseous constituents (e.g.,gaseous constituents in a tobacco smoke stream).

The modified activated carbon can filter one or more selectedconstituents from mainstream smoke. The term “mainstream” smoke includesthe mixture of gases passing down the tobacco rod and issuing throughthe filter end. i.e., the amount of smoke issuing or drawn from themouth end of a smoking article during smoking of the smoking article.The mainstream smoke contains smoke that is drawn in through both thelit region of the smoking article, as well as through the paper wrapper.

The activated carbon can be selected to have an appropriate surface areato preferentially adsorb selected constituents from cigarette smoke.Activated carbon typically has a surface area greater than about 50 m²/g(e.g., at least about 100, 200, 500, 1000 or 2000 m²/g). Typically, theabsorptive capacity of activated carbon increases with increasingsurface area. Furthermore, surface area increases with decreasingparticle size. When used as cigarette filter material, however,activated carbon particles having a small particle size may packtogether too densely to permit mainstream smoke to flow through thefilter with desired resistance to draw (RTD) during smoking. On theother hand, if the particle size is too large there may be insufficientsurface area to accomplish the desired degree of filtration. Therefore,such factors can be taken into account in selecting an activated carbonhaving a particular particle size.

A particularly preferred activated carbon is commercially available(e.g., from PICA USA, Inc., Truth or Consequences, N. Mex.). Theactivated carbon could also be manufactured via the carbonization ofcoconut husk, coal, wood, pitch, peat, cellulose fibers, lignite andolive pits. Carbonization is usually carried out at elevatedtemperatures, e.g., 400-1000° C. in an inert atmosphere, followed byactivation (i.e., calcining) typically in an atmosphere of steam orcarbon dioxide. The activated carbon substrate can be in the form ofbeads, granules and/or fibers.

The pre-treatment can modify an exposed surface of the activated carbon.During the pre-treatment, a compound in solution is absorbed and/oradsorbed by the activated carbon, e.g., the pre-treatment compound canbe incorporated on the exterior and/or interior surfaces of theactivated carbon. The pre-treatment compound, which is used to renderthe exposed surface(s) of the activated carbon substantiallyhydrophilic, is preferably a surfactant (i.e., amphiphilic compound).

Surfactants are typically organic compounds that contain both ahydrophobic moiety and a hydrophilic moiety. The surfactant can be ananionic, an amphoteric, a zwitterionic, a nonionic, or a cationicsurfactant, or combinations thereof. A preferred pre-treatment compoundis cetyltrimethylammonium chloride. For example a 10 wt. % solution ofcetyltrimethylammonium chloride in water can be incorporated onto theactivated carbon by immersing the activated carbon in the solution.

The surfactant can be an anionic compound. Suitable anionic compoundsinclude but are not limited to alkyl sulfates, alkyl ether sulfates,alkyl or alkaryl sulfonates, alkyl succinates, alkyl sulfosuccinates,alkyl phosphates, alkyl ether phosphates, alkyl ether carboxylates,alkylamino acids, alkyl peptides, carboxylic acids, acyl and alkylglutamates, alkyl isethionates, and alpha-olefin sulfonates, especiallytheir sodium, potassium, magnesium, ammonium and mono-, di- andtriethanolamine salts. The alkyl groups generally contain from 8 to 18carbon atoms and may be saturated or unsaturated. The alkyl ethersulfates, alkyl ether phosphates and alkyl ether carboxylates maycontain from 1 to 10 ethylene oxide or propylene oxide units permolecule, and preferably contain 1 to 3 ethylene oxide units permolecule.

Examples of suitable anionic surfactants include sodium and ammoniumlauryl ether sulfate (with 1, 2, and 3 moles of ethylene oxide), sodium,ammonium, and triethanolamine lauryl sulfate, disodium laurethsulfosuccinate, sodium cocoyl isethionate, sodium C12-14 olefinsulfonate, sodium laureth-6 carboxylate, sodium C12-15 pareth sulfate,sodium methyl cocoyl taurate, sodium dodecylbenzene sulfonate, sodiumcocoyl sarcosinate, triethanolamine monolauryl phosphate, and fatty acidsoaps.

Nonionic surfactants can include but are not limited to aliphatic(C₆-C₁₈) primary or secondary linear or branched chain acids, alcoholsor phenols, alkyl ethoxylates, alkyl phenol alkoxylates (especiallyethoxylates and mixed ethoxypropoxy), block alkylene oxide condensatesof alkyl phenols, alkylene oxide condensates of alkanols, ethyleneoxide/propylene oxide block copolymers, semi-polar nonionics (e.g.,amine oxides and phosphine oxides), as well as alkyl amine oxides. Othersuitable nonionics include mono- or di-alkyl alkanolamides and alkylpolysaccharides, sorbitan fatty acid esters, polyoxyethylene sorbitanfatty acid esters, polyoxyethylene sorbitol esters, polyoxyethyleneacids, and polyoxyethylene alcohols. Examples of suitable nonionicsurfactants include coco-mono- or di-ethanolamide, coco-di-glucoside,alkyl polyglucoside, polysorbate 20, ethoxylated linear alcohols,cetearyl alcohol, lanolin alcohol, stearic acid, glyceryl stearate,PEG-100 stearate, and oleth 20.

The surfactant can be an amphoteric or zwitterionic surfactant.Amphoteric and zwitterionic surfactants are those compounds which havethe capacity of behaving either as an acid or a base. Examples ofamphoteric surfactants include C₈ to C₁₈ sultaines such as coco-sultaineand cocoamidopropyl hydroxysultaine; C₈ to C₁₈ fatty derivatives ofamino acids such as cocoamphocarboxyglycinate and lauramphoglycinate; C₈to C₁₈ alkyl betaines such as decyl betaine, coco-betaine, laurylbetaine, myristyl betaine and stearyl betaine; and C₈ to C₁₈ amidoalkylbetaines such as cocoamidoethyl betaine, cocoamidopropyl betaine,lauramidopropyl betaine, myristamidopropyl betaine and oleamidopropylbetaine

The surfactant can be a cationic surfactant. Suitable cationicsurfactants include but are not limited to alkyl amines, alkylimidazolines, ethoxylated amines, quaternary compounds, and quaternizedesters. In addition, alkyl amine oxides can behave as a cationicsurfactant at a low pH. Examples include lauramine oxide,dicetyldimonium chloride and cetrimonium chloride.

An aqueous or other solvent solution of the pre-treatment compound canbe sprayed onto the activated carbon, or the activated carbon may beimmersed in the solution. “Aqueous” as used herein refers to mixtures(e.g., solutions and emulsions) that comprise water as a component. Anaqueous mixture can also include organic solvents, which are eithermiscible or immiscible with water. The concentration of thepre-treatment compound in the solvent can be from about 1 to 99 wt. %. Apreferred solution of the pre-treatment compound comprises from about 1to 25 wt. %, more preferably from about 1 to 10 wt. %, of thepre-treatment compound in a suitable solvent. Suitable solvents includepropylene glycol, alcohols (e.g., methyl alcohol, ethyl alcohol, etc.),water, glycerin and mixtures thereof. A preferred solvent for thepre-treatment compound is water. After coating the activated carbonsubstrate with a solution of the pre-treatment compound, the pre-treatedactivated carbon substrate can be air dried and/or dried in an oven atlow temperature (e.g., less than about 120° C., preferably about 100°C.) to form pre-treated activated carbon. The pre-treatment compound ispreferably incorporated over an exposed surface of the activated carbonsubstrate and, after drying, results in an activated carbon substratehaving a surface (i.e., an exposed surface on the interior and exteriorof the activated carbon substrate) that is substantially hydrophilic.

A solution comprising the carbon precursor can be incorporated in and/oron the pre-treated activated carbon substrate. As described below, anaqueous or other solvent solution of the carbon precursor can be sprayedonto the pre-treated activated carbon, or the pre-treated activatedcarbon may be immersed in the carbon precursor solution. The carbonprecursors are preferably organic compositions. Particularly preferredcarbon precursors are saccharides, for example pentose and hexose;monosaccharides such as glucose; and disaccharides, especially sucrose.Additional carbon precursors include polysaccharides, fructose and ethylcellulose.

A solution comprising the carbon precursor compound used in making themodified activated carbon may be absorbed and/or adsorbed by thepre-treated activated carbon, e.g., the carbon precursor compound can beincorporated on the exterior and/or interior surfaces of the activatedcarbon substrate. By providing a pre-treated activated carbon substrate,an aqueous solution of a carbon precursor can form a uniform coating ofthe carbon precursor on the activated carbon substrate.

Preferably, the carbon precursor compound does not substantiallypenetrate into the pores of the activated carbon substrate. Rather, thecarbon precursor compound preferably forms a uniform coating over theexposed surface of the activated carbon which, upon decomposition of thecarbon precursor, forms a uniform porous carbon coating capable ofmediating absorption and/or adsorption by the activated carbonsubstrate.

The carbon precursor can be incorporated in and/or on the activatedcarbon particles using a fluidized bed or, alternatively, the carbonprecursor can be sprayed onto the activated carbon, or the activatedcarbon can be immersed in a solution comprising the carbon precursor.

The carbon precursor is preferably added in amounts of about 1 to 150%,preferably at least about 10% (e.g., at least 20, 40, 60 or 80%±5% byweight) of the original weight of the activated carbon. Prior tocarbonizing the carbon precursor, the carbon precursor coatingsubstantially covers the activated carbon substrate (i.e., the carbonprecursor coating substantially blocks all of the surface porosity ofthe activated carbon).

The activated carbon substrate and the carbon precursor solution arepreferably mixed at about room temperature, though suitable temperaturesrange from about 0° C. to 80° C. After the carbon precursor solution isincorporated in and/or on the activated carbon substrate, the coatedactivated carbon is dried at about 80 to 120° C., preferably at about100° C., and then heated at a temperature of about 150 to 400° C. for aperiod of from about 1 minute to 72 hours in order to carbonize thecarbon precursor and form the modified activated carbon. Carbonizationof the carbon precursor coating can create a porous carbon coating.Preferably the carbon coating formed from the carbon precursor will havean average surface pore size that is different than, more preferablyless than, the average surface pore size of the activated carbonsubstrate. For example, the average surface pore size of the modifiedactivated carbon can be at least 10, 15, 20 or 25% less than the averagesurface pore size of the activated carbon substrate. In a preferredembodiment, the carbon membrane of the modified activated carbon has anaverage pore size that is at least 25% less than the average surfacepore size of the activated carbon substrate. By changing the surfaceporosity of the activated carbon substrate, the absorption and/oradsorption kinetics of the activated carbon can be changed.

For large quantities, the modified activated carbon can be made by thefollowing process, wherein a fluidizing bed is used to apply at leastone of the pre-treatment compound and the carbon precursor onto theactivated carbon substrate (e.g., particles of activated carbon). In theprocess, activated carbon particles are introduced into a vessel. Inorder to fluidize the particles, a gas such as nitrogen is introducedinto the bottom of the vessel. A solution of the pre-treatment compoundor carbon precursor is then introduced into the vessel while the carbonparticles are in a fluidized state. Preferably, these materials areincorporated onto an exposed surface of the activated carbon substratewhile maintaining the particles at ambient temperature, i.e., theprocess is carried out without heating the particles. Although thematerials are preferably applied to the upper surface of the fluidizedbed, the agitation of the carbon particles distributes the materialsthroughout the bed of carbon particles.

In the fluidizing treatment, an inert gas such as nitrogen is used tofluidize the activated carbon particles. The flow rate of the fluidizinggas will depend on the size of the fluidized bed. In a preferredembodiment, the flow rate is at least 5 ft³/minute, more preferably 10to 20 ft³/minute. The flow rate of the carbon precursor onto the carbonparticles will depend on the amount of carbon being treated and/or theduration of the fluidized bed treatment. In a preferred embodiment, thecarbon precursor is applied as a liquid at a flow rate of at least 10g/minute, e.g., 15 to 25 g/minute for a batch of 25 pounds of activatedcarbon. The carbon precursor can be dissolved or suspended in a carriersuch as propylene glycol, alcohols (e.g., methyl alcohol, ethyl alcohol,etc.), water, glycerin and mixtures thereof, e.g., an aqueous solutioncontaining the carbon precursor and water. The concentration of carbonprecursor in the carrier can be from about 1 to 99% by weight. Apreferred concentration of carbon precursor is from about 20 to 60% byweight. After the carbon precursor is applied to the carbon in thefluidized bed, the fluidizing action can be continued to promotethorough distribution of the precursor in the fluidized bed. As anexample, the carbon precursor can be applied to activated carbonparticles for a period of 15 minutes and the fluidizing action can becontinued for an additional 5 minutes thereafter. While not wishing tobe bound by theory, it is believed that the fluidizing gas is effectivein causing the carbon precursor to be distributed uniformly over thecarbon particles via mass transfer and/or particle collisions.

Any suitable vessel that is capable of maintaining the activated carbonparticles in a fluidized state may be used. Such vessels can be designedas batch or continuous processing apparatus. An exemplary batch typefluidized bed arrangement is shown in FIG. 1 and an exemplary continuoustype fluidized bed arrangement is shown in FIG. 2. A highly advantageousfeature of the fluidized bed technique of applying the carbon precursorto the pre-treated activated carbon substrate is that a uniform coatingof the carbon precursor can be obtained on the activated carbonsubstrate. In the description that follows, incorporation of the carbonprecursor in and/or on the activated carbon is described using afluidized bed. A fluidized bed arrangement can also be used toincorporate a solution of the pre-treatment compound in and/or on theactivated carbon.

In the FIG. 1 arrangement, a vessel 210 is loaded with activated carbon212 and a fluidizing gas flows upwardly through openings in adistribution plate 214. The gas preferably comprises an inert gas suchas nitrogen supplied through supply line 216. After passing through thebed of carbon particles, the fluidizing gas passes through filters 220,222 and is removed from the vessel through exhaust line 218. The carbonparticles can be supplied into the vessel 210 through feed port 224. Toclean off accumulated material such as fine carbon particles, a clearinggas such as nitrogen can be blown back through the filters 220, 222 viasupply line 226. A series of valves can be used to isolate the exhaustline 218 from the supply line 226 whereby nitrogen is prevented fromflowing into supply line 226 when gasses are withdrawn through exhaustline 218. Likewise, the valves can isolate the exhaust line 218 from theblow back gas supplied by supply line 226 during cleaning of the filters220, 222. The filter cleaning can be conducted during treatment of thecarbon, e.g., nitrogen blow back can be carried out periodically whilethe activated carbon is in a fluidized state. As an example, if thecarbon is treated for 15 minutes, the nitrogen blow back can be carriedout in 2 second pulses every 60 seconds during the carbon treatment. Asolution of the carbon precursor in tank 228 can be removed by a pump230 which sends the precursor through supply line 232 and into thevessel after passing through nozzles 234, 236. The pretreated and coatedactivated carbon particles can be removed from the vessel through adischarge line 238.

In the FIG. 2 arrangement, a compartmented vessel 240 is loaded withactivated carbon 242 and a fluidizing gas flows upwardly throughopenings in a distribution plate (not shown). The gas preferablycomprises nitrogen supplied through supply line 246. After passingthrough the bed of carbon particles, the fluidizing gas passes throughfilters 250, 251, 252, 253 and is removed from the vessel throughexhaust line 248. The carbon particles can be supplied into the vessel240 through feed line 254.

To clean off accumulated material such as fine carbon particles, aclearing gas such as nitrogen can be blown back through the filters 250,252 via supply line 256. A series of valves can be used to isolate theexhaust line 248 from the supply line 256 whereby nitrogen is preventedfrom flowing into supply line 256 when gasses are withdrawn throughexhaust line 248. Likewise, the valves can isolate the exhaust line 248from the blow back gas supplied by supply line 256 during cleaning ofthe filters 250-253. The filter cleaning can be conducted duringtreatment of the carbon, e.g., nitrogen blow back can be carried outperiodically while the carbon is in a fluidized state. As an example, ifthe carbon is treated for 15 minutes, the nitrogen blow back can becarried out in 2 second pulses every 60 seconds during the carbontreatment.

A carbon precursor solution in tank 258 can be removed by a pump 260which sends the precursor solution through supply line 262 and into thevessel after passing through nozzles 264, 265, 266, 267. The coatedactivated carbon can be removed from the vessel through a discharge line268. The vessel 240 can have any desired number of compartments, e.g.,in the embodiment shown the vessel includes six compartments 270, 272,274, 276, 278, 280 separated by partitions 282, 284, 286, 288, 290. Thecarbon precursor can be supplied only to the middle compartments 272,274, 276, 278 whereby the first compartment 270 can be used as a loadingcompartment and the last compartment 280 can be used as a dischargecompartment.

Passage of carbon particles from one compartment to the next is achievedby providing one or more openings in the partitions 282, 284, 286, 288,290. For example, a single opening can be provided at the bottom of eachpartition, e.g., a rectangular opening of 1-2 inches by 2-4 inches. Toprevent the carbon particles from flowing directly from one compartmentto the next, it is advantageous to offset the openings, e.g., the firstpartition 282 can have an opening near one side of the vessel and thenext partition 284 can have an opening near the opposite side of thevessel and so on to provide a tortuous path of travel of the carbonthrough the vessel.

The fluidized bed of carbon particles behaves like a liquid with aportion of the fluidized particles being driven upwardly by thefluidizing gas with some of the particles being transferred from thefirst compartment 270 into the second compartment 272 by flowing throughan opening (e.g., 1 by 2 inch opening) between the compartments 270, 272at the bottom of the partition 282. In like manner, the particles movefrom compartment to compartment until they reach the dischargecompartment. Thus, the particles move from compartment to compartmentwhile in a fluidized state and ultimately are removed from the vesselafter a predetermined residence time. The residence time can varydepending on the size of the vessel and number of compartments. Theresidence time can range from 5 to 60 minutes, more preferably 10 to 20minutes.

The sizes of the compartments of the vessel are preferably the same andthe carbon precursor can be distributed in the middle compartments bytwo or more outlets in each compartment. The carbon precursor ispreferably supplied to each compartment at a flow rate which achievesuniform distribution of the carbon precursor on the activated carbonparticles. For example, the carbon precursor can be supplied at a flowrate which results in a liquid drops, spray of liquid, or continuousflow of liquid onto the bed of fluidized particles. While not wishing tobe bound by theory, it is believed that uniform distribution of thecarbon precursor is assisted by the fluidizing gas which aids masstransfer of precursor from particle to particle as the particles travelin vertical and/or horizontal directions in the fluidized bed. Apreferred outlet arrangement provides one outlet for distributing thecarbon precursor over an area of 20 to 60 in², e.g., about 30 to 40 in²at the upper surface of the fluidized bed.

The carbon precursor can be applied to the fluidized particles at anydesired temperature. Preferably, the bed is not heated and the particlescan be at a temperature in the range of about 0 to 80° C., morepreferably about 15 to 30° C. Heating of the carbon particles during thetreatment is not required because adequate coating of the particles withthe carbon precursor can be achieved without heating. Preferably,substantially all of the carbon precursor introduced into the vessel iscoated on the carbon particles. In terms of added weight, the carbonparticles can be treated to include from about 1 to 150 wt. % (dryweight) of the carbon precursor.

As mentioned above, the incipient wetness technique can be used toincorporate a solution of the pre-treatment compound and/or a solutionof the carbon precursor into and/or on the activated carbon substrate.For example, activated carbon particles can be immersed in an aqueous ornon-aqueous solution of a carbon precursor for a specified period oftime and then dried to incorporate a coating of the precursor on anexposed surface of the particles. The period of time is preferablychosen so as to be sufficient to form a substantially uniform coating ofthe compound in and/or on the carbon (e.g., from about 1 to 48 hours,preferably about 12 to 24 hours). A preferred concentration of asolution comprising the pre-treatment compound is from about 1 to 25 byweight, and a preferred concentration of the carbon precursor solutionis from about 20 to 60% by weight. While the activated carbon isimmersed in the solvent containing the precursor solute, the precursoris absorbed and/or adsorbed in and/or on the activated carbon (e.g.,onto the exposed surface of the activated carbon). The carbon precursorcan be incorporated into the activated carbon substrate in a singlecoating step or in multiple coating steps.

After the carbon precursor solution is incorporated in and/or on theactivated carbon substrate, the coated carbon is dried preferably byair-drying or by heating at a temperature of from about 80 to 120° C.After drying, the coated activated carbon is heated at a temperaturesufficient to carbonize (i.e., thermally decompose) the carbon precursorand form a carbon coating.

The heating time and temperature will depend, at least in part, on theactivated carbon substrate, the carbon precursor and the desiredstructure of the modified activated carbon. Modified activated carbon ispreferably formed by heating the coated activated carbon at atemperature of less than about 400° C., more preferably less than about300° C., for a time of less than about 2 hours, though highertemperatures and/or longer times can be used. Preferably the thermalbudget (i.e., time and temperature) used to decompose the carbonprecursor is sufficient to convert substantially all of the carbonprecursor to carbon.

The coated activated carbon substrate can be heated in an oxidizing orinert atmosphere. An oxidizing atmosphere can comprise O₂, CO, air andmixtures thereof. An inert atmosphere can comprise N₂, Ar, He andmixtures thereof. Without wishing to be bound by theory, it is believedthat heating in an oxidizing atmosphere, which causes the decompositionand oxidation of the carbon precursor, creates a larger mean surfaceporosity than heating in an inert atmosphere wherein the carbonprecursor decomposes but does not as readily oxidize.

SEM micrographs of as-received activated carbon and modified activatedcarbon are shown in FIGS. 3 and 4, respectively. FIGS. 3A and 3B showas-received PICA carbon. To form the modified activated carbon shown inFIGS. 4A and 4B, the as-received activated carbon was initially immersedin a 10 wt. % solution of cetyltrimethylammonium chloride, air dried atroom temperature and then oven dried at 100° C. for 5 hours to form apre-treated activated carbon. The modified activated carbon was preparedby immersing 20 g of the pre-treated activated carbon with 10 g of a 67wt. % solution of sucrose in water for 12 hours to form a coated carbon,drying the coated carbon at 100° C. for about 5 hours, and then heatingthe coated carbon at 300° C. for 1 hour. The surface area of themodified activated carbon after heating at 300° C. in nitrogen is about80 m²/g.

The activated carbon particles can be provided with a loading of about 1to 150% by weight of the carbon. Without wishing to be bound by theory,it is believed that the total surface area (as measured by BET) of themodified activated carbon will be dominated by the micro-porosity of theactivated carbon substrate. Because the porous carbon coating does notsubstantially block access to the micropores, the total surface area ofthe modified activated carbon is substantially equal to the totalsurface area of the activated carbon substrate. Preferably, the totalsurface area of the modified activated carbon is at least 90%, morepreferably at least 95% of the total surface area of the activatedcarbon substrate. While the total surface area of the activated carbonis preferably not substantially reduced, the incorporation of a uniformporous carbon membrane can alter, preferably decrease, the averagesurface pore size of the modified activated carbon with respect to theactivated carbon substrate. The absorption/adsorption characteristics ofthe activated carbon can be controlled by controlling the pore sizedistribution (e.g., average surface porosity) in the carbon coating.Furthermore, by pre-treating the activated carbon (i.e., converting atypically hydrophobic carbon surface to a substantially hydrophilicsurface) a uniform coating of the carbon precursor can be formed on theactivated carbon substrate. A uniform carbon membrane covers at least80% of the exposed surface (i.e., line-of-sight external surface) of theactivated carbon substrate, more preferably at least 90% of the exposedsurface and/or has an average thickness having a standard deviation thatis less than about 25%, more preferably less than about 10%, of theaverage thickness.

The application of a carbon membrane can impart mechanical robustness tothe activated carbon substrate. For example, by applying a carbonmembrane to the activated carbon substrate the propensity for flaking ordusting of the activated carbon substrate can be reduced. Preferably theaverage thickness of the carbon membrane is between about 1 micron and0.1 mm (e.g., from about 1-5, 2-20, 5-50, 10-20, 40-60, 50-100, or80-100 microns).

The modified activated carbon can have improved filtrationcharacteristics relative to the activated carbon substrate. The carbonmembrane can be applied in a manner which allows the modified activatedcarbon to reduce the content in mainstream smoke of one or more gaseousconstituents such as 1,3-butadiene, acrolein, isoprene, propionaldehyde,acrylonitrile, benzene, toluene, styrene, acetaldehyde and hydrogencyanide. Preferably, however, the modified activated carbon does notsubstantially reduce the concentration in mainstream smoke of flavorcomponents of the smoke. Thus, the modified activated carbon can exhibita decreased retentive capacity relative to the activated carbonsubstrate via the incorporation of a uniform porous carbon membrane thatchanges the absorption and/or adsorption kinetics of the activatedcarbon substrate. An unmodified activated carbon substrate that isincorporated into a cigarette can remove desirable flavor compoundsand/or impart an undesirable carbon flavor to cigarette smoke duringsmoking of the cigarette. Advantageously, the uniform coating of themodified activated carbon can substantially eliminate the adverse tasteassociated with activated carbon.

FIG. 5 shows the percentage reduction relative to a standard for threegaseous constituents (1,3-butadiene, acrolein, benzene) usingas-received activated carbon (corresponding to the data at 0% sucrose)or modified activated carbon in an experimental set up. Thesucrose/carbon ratio refers to the weight gain (in weight %) of theactivated carbon substrate from the decomposition of a sucrose coatingto form the modified activated carbon. To produce the modified activatedcarbon, a 10 wt. % solution of cetyltrimethyl-ammonium chloride wascombined with as-received PICA activated carbon, dried in air and thendried at 100° C. for about 5 hours to form a pre-treated activatedcarbon. Approximately 20 g of the pre-treated activated carbon wascombined with 10 g of a 67 wt. % aqueous solution of sucrose via theincipient wetness technique. After a 12 hour exposure, the mixture wasdried at 100° C. for 5 hours and then heated at 300° C. for 1 hour toform the modified activated carbon. By re-immersing the modifiedactivated carbon in the sucrose solution, the loading of carbon on theactivated carbon substrate (expressed wt. %/wt. %) was increased.

Referring still to FIG. 5, the percent reduction of 1,3-butadiene,acrolein and benzene improved for carbon coating additions up to about65%. A carbon coating corresponding to a weight gain of about 135%,however, resulted in a decreased filtration efficiency for1,3-butadiene, acrolein and benzene.

The modified activated carbon may be used in a variety of applications,including cigarettes, cut filler compositions and cigarette filters. Ina cigarette comprising the modified activated carbon, the modifiedactivated carbon particles may be located in the filter and/or dispersedin the cut filler. A typical cigarette will include from about 10 mg toabout 200 mg of the modified activated carbon particles, although theamount needed can also be determined by routine experimentation and/oradjusted accordingly. The modified activated carbon can be used toselectively adsorb/filter specific constituents from the mainstreamsmoke of a cigarette.

Examples of suitable types of tobacco materials which may be usedinclude flue-cured, Burley, Bright, Maryland or Oriental tobaccos, therare or specialty tobaccos, and blends thereof. The tobacco material canbe provided in the form of tobacco lamina; processed tobacco materialssuch as volume expanded or puffed tobacco, processed tobacco stems suchas cut-rolled or cut-puffed stems, reconstituted tobacco materials; orblends thereof. Tobacco substitutes may be used.

In cigarette manufacture, the tobacco is normally employed in the formof cut filler, i.e., in the form of shreds or strands cut into widthsranging from about 1/10 inch to about 1/20 inch or even 1/40 inch. Thelengths of the strands range from between about 0.25 inches to 3.0inches. The cigarettes may further comprise one or more flavorants orother additives (e.g., burn additives, combustion modifying agents,coloring agents, binders, etc.).

Techniques for cigarette manufacture are known in the art, and may beused to incorporate the modified activated carbon. The resultingcigarettes can be manufactured to any desired specification usingstandard or modified cigarette making techniques and equipment. Thecigarettes may range from about 50 mm to 120 mm in length. Thecircumference is from about 15 mm to 30 mm in circumference, andpreferably around 25 mm. The packing density is typically between therange of about 100 mg/cm³ to 300 mg/cm³, and preferably about 150 mg/cm³to 275 mg/cm³.

Any conventional or modified cigarette filter may incorporate themodified activated carbon particles. The modified activated carbon canincorporated into or onto a support such as paper (e.g., liner, plugwrap or tipping paper) that is located along a filter portion of acigarette. The modified activated carbon can also be loaded onto asupport such as lightly or tightly folded paper inserted into a hollowportion of the cigarette filter. The support is preferably in the formof a sheet material such as crepe paper, filter paper, or tipping paper.However, other suitable support materials such as organic or inorganiccigarette compatible materials can also be used.

FIG. 6 illustrates a cigarette 2 having a tobacco rod 4, a filterportion 6, and a mouthpiece filter plug 8. Modified activated carbonparticles can be loaded onto folded paper 10 inserted into a hollowcavity such as the interior of a free-flow sleeve 12 forming part of thefilter portion 6. The paper 10 can be used in forms other than as afolded sheet. For instance, the paper 10 can be deployed as one or moreindividual strips, a wound roll, etc. In whichever form, a desiredamount of modified activated carbon particles can be provided in thecigarette filter portion by adjusting the amount of modified activatedcarbon coated per unit area of the paper and/or the total area of coatedpaper employed in the filter (e.g., higher amounts of surface-modifiedadsorbent can be provided simply by using larger pieces of coatedpaper). In the cigarette shown in FIG. 6, the filter portion 6 may beheld together by filter overwrap 11, and the tobacco rod 4 and thefilter portion 6 can be joined together with tipping paper 14.

The modified activated carbon can be incorporated into the filter paperin a number of ways. For example, the modified activated carbon can bemixed with water to form a slurry. The slurry can then be coated ontopre-formed filter paper and allowed to dry. The filter paper can then beincorporated into the filter portion of a cigarette in the manner shownin FIG. 6. Alternatively, dried paper comprising the modified activatedcarbon can be wrapped into a plug shape and inserted into a filterportion of the cigarette. For example, the paper can be wrapped into aplug shape and inserted as a plug into the interior of a free-flowfilter element such as a polypropylene or cellulose acetate sleeve. Inanother arrangement, the paper can comprise an inner liner of such afree-flow filter element.

The modified activated carbon can be added to filter paper during thepaper-making process. For example, the modified activated carbon can bemixed with bulk cellulose to form a cellulose pulp mixture. The mixturecan be then formed into filter paper.

The modified activated carbon can incorporated in a hollow portion of acigarette filter. For example, some cigarette filters have aplug/space/plug configuration in which the plugs comprise a fibrousfilter material (e.g., polypropylene or cellulose acetate fibers) andthe space is simply a void between the two filter plugs. That void canbe filled with the modified activated carbon. The modified activatedcarbon can be used in granular form or loaded onto a suitable supportsuch as a fiber or thread (e.g., the modified activated carbon can beincorporate in a plug of cellulose acetate tow material).

FIG. 7 shows a cigarette 2 comprised of a tobacco rod 4 and a filterportion 6 in the form of a plug-space-plug filter having a mouthpiecefilter 8, a plug 16, and a space 18. The plug can comprise a tube orsolid piece of material such as polypropylene or cellulose acetatefibers. The tobacco rod 4 and the filter portion 6 are joined togetherwith tipping paper 14. The filter portion 6 may include a filteroverwrap 11. Modified activated carbon particles can be incorporated inand/or on the filter overwrap 11 such as by being coated thereon.Alternatively, the modified activated carbon particles can beincorporated in the mouthpiece filter 8, in the plug 16 and/or in thespace 18. Moreover, the modified activated carbon can be incorporated inany element of the filter portion of a cigarette.

In another embodiment, the modified activated carbon is employed in afilter portion of a cigarette for use with a smoking device as describedin U.S. Pat. No. 5,692,525, the entire content of which is herebyincorporated by reference. FIG. 8 illustrates one type of constructionof a cigarette 100 which can be used with an electrical smoking device.As shown, the cigarette 100 includes a tobacco rod 60 and a filterportion 62 joined by tipping paper 64. The filter portion 62 preferablycontains a tubular free-flow filter element 102 and a mouthpiece filterplug 104. The free-flow filter element 102 and mouthpiece filter plug104 may be joined together as a combined plug 110 with plug wrap 112.The tobacco rod 60 can have various forms incorporating one or more ofthe following items: an overwrap 71, another tubular free-flow filterelement 74, a cylindrical tobacco plug 80 preferably wrapped in a plugwrap 84, a tobacco web 66 comprising a base web 68 and tobacco flavormaterial 70, and a void space 91. The free-flow filter element 74provides structural definition and support at the tipped end 72 of thetobacco rod 60. At the free end 78 of the tobacco rod 60, the tobaccoweb 66 together with overwrap 71 are wrapped about cylindrical tobaccoplug 80. Various modifications can be made to a filter arrangement forsuch a cigarette incorporating the modified activated carbon.

In such a cigarette, the modified activated carbon can be incorporatedin various ways such as by being loaded onto paper or other substratematerial that is fitted into the passageway of the tubular free-flowfilter element 102 therein. The modified activated carbon may also bedeployed as a liner or a plug in the interior of the tubular free-flowfilter element 102. Alternatively, or in addition, the modifiedactivated carbon can be incorporated into the fibrous wall portions ofthe tubular free-flow filter element 102 itself. For instance, thetubular free-flow filter element or sleeve 102 can be made of suitablematerials such as polypropylene or cellulose acetate fibers and themodified activated carbon can be mixed with such fibers prior to or aspart of the sleeve forming process.

The modified activated carbon can be incorporated into the mouthpiecefilter plug 104 instead of in the element 102. However, as in thepreviously described embodiments, the modified activated carbon may beincorporated into more than one component of a filter portion such as bybeing incorporated into the mouthpiece filter plug 104 and into thetubular free-flow filter element 102. The filter portion 62 of FIG. 8can be modified to create a void space into which the modified activatedcarbon particles can be inserted.

As explained above, the modified activated carbon can be incorporated invarious support materials. When the modified activated carbon particlesare used in filter paper, the particles may have an average particlesize of 10 to 100 microns, preferably 30 to 80 microns. When thesurface-modified adsorbent is used in filter fibers or other mechanicalsupports, larger particles may be used. Such particles preferably have amesh size from 10 to 70, and more preferably from 20 to 50 mesh.

The amount of modified activated carbon employed in the cigarette filterby way of incorporation on a suitable support such as filter paperand/or filter fibers depends on the amount of constituents in thetobacco smoke and the amount of constituents desired to be removed. Asan example, the filter paper and the filter fibers may contain from 10%to 50% by weight of the modified activated carbon particles.

While preferred embodiments have been described, it is to be understoodthat variations and modifications may be resorted to as will be apparentto those skilled in the art. Such variations and modifications are to beconsidered within the purview and scope of the claims appended hereto.

All of the above-mentioned references are herein incorporated byreference in their entirety to the same extent as if each individualreference was specifically and individually indicated to be incorporatedherein by reference in its entirety.

What is claimed is:
 1. A modified activated carbon comprising anactivated carbon substrate and a uniform porous carbon membrane formedon an exposed surface of the activated carbon substrate.
 2. The modifiedactivated carbon of claim 1, wherein the modified activated carbon is inthe form of beads, granules or fibers.
 3. The modified activated carbonof claim 1, wherein the carbon membrane comprises from about 1 to 150%by weight of the activated carbon substrate.
 4. The modified activatedcarbon of claim 1, wherein the carbon membrane comprises from about 20to 80% by weight of the activated carbon substrate.
 5. The modifiedactivated carbon of claim 1, wherein the carbon membrane has a surfaceporosity at least 10% different than the surface porosity of theactivated carbon substrate.
 6. The modified activated carbon of claim 1,wherein the carbon membrane has a mean surface porosity at least 25%less than the mean surface porosity of the activated carbon substrateand/or the modified activated carbon has an average surface area of atleast 50 m²/g or at least 200 m²/g.
 7. The modified activated carbon ofclaim 1, wherein the carbon membrane covers at least 80% of the exposedsurface of the activated carbon substrate and/or the carbon membrane hasan average thickness having a standard deviation that is less than about25% of the average thickness.
 8. The modified activated carbon of claim1, wherein the carbon membrane has an average thickness of from about 1micron to 0.1 mm.
 9. A cigarette comprising activated carbon particleswherein the modified activated carbon particles are dispersed in tobaccocut filler and/or located in a filter element of the cigarette, theactivated carbon particles comprising an activated carbon substrate anda uniform porous carbon membrane formed on an exposed surface of theactivated carbon substrate.
 10. The cigarette of claim 9, wherein thecarbon membrane comprises from about 1 to 150% by weight of theactivated carbon substrate.
 11. The cigarette of claim 9, wherein thecarbon membrane comprises from about 20 to 80% by weight of theactivated carbon substrate.
 12. The cigarette of claim 9, wherein thecarbon membrane has a surface porosity at least 10% different than thesurface porosity of the activated carbon substrate.
 13. The cigarette ofclaim 9, wherein the carbon membrane has a mean surface porosity atleast 25% less than the mean surface porosity of the activated carbonsubstrate and/or the modified activated carbon has an average surfacearea of at least 50 m²/g or at least 200 m²/g.
 14. The cigarette ofclaim 9, wherein the carbon membrane covers at least 80% of the exposedsurface of the activated carbon substrate and/or the carbon membrane hasan average thickness having a standard deviation that is less than about25% of the average thickness.
 15. The cigarette of claim 9, wherein thecarbon membrane has an average thickness of from about 1 micron to 0.1mm.
 16. The cigarette of claim 9, wherein the activated carbon particlesare incorporated in filler paper and have an average particle size of 10to 100 microns.
 17. The cigarette of claim 9, wherein the cigaretteincludes about 10 to about 200 mg of the activated carbon particles. 18.The cigarette of claim 9, wherein the activated carbon substrate is asubstrate selected from the group consisting of beads, granules andfibers and/or the activated carbon substrate has an average particlesize of from about 100 microns to 5 mm or from about 200 microns to 2mm.
 19. The cigarette of claim 9, wherein the activated carbon substratehas an average pore size of less than about 500 Angstroms, the activatedcarbon substrate has a pore size distribution comprising greater thanabout 20% micropores and fewer than about 80% mesopores and/or theactivated carbon substrate has an average surface area of greater than50 m²/g or greater than 200 m²/g.